We propose to investigate certain biochemical and biophysical events associated with the stepwise activation of the amphibian oocyte following steroid stimulation of the resumption of meiotic maturation. The approach will be to examine: 1. The sequence of membrane associated events initiated by the direct action of progesterone (and other steroids) on the oocyte plasma membrane. Membrane events include membrane potential, membrane conductance to specific ions (Na ion, K ion, Ca2 ion, and Cl minus), and calcium binding. 2. The possible role of calcium as a second messenger for steroid in the release of the prophase block. 3. The link(s) between membrane event, calcium, and changes in translational control during meiotic maturation. Changes in translational control include the appearance of the "maturation promoting factor" and an increase in protein synthesis prior to germinal vesicle breakdown. One possible link involves the interaction between calcium, cyclic GMP, and cyclic AMP following steroid induction. 4. Possible feed-back control of membrane events by cytoplasmic factors such as the "maturation promoting factor" or the "chromosome condensing factor."